The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Known portable power tools typically have an electric motor received within a tool housing. One common type of electric motor used in power tools has a rotor, a stator, and brushes. The rotor includes a rotor shaft, laminations mounted on the rotor shaft, armature windings wound in slots in the lamination stack, and a commutator mounted on the rotor shaft and electrically connected to the armature windings. The stator may have field windings wound in laminations, or may have permanent magnets. The brushes are mounted in brush housings, often known as brush boxes or brush holders, in sliding electrical contact with the commutator. Electric current is supplied from a power source through the brushes to the commutator, and from the commutator to the armature windings.
The brushes and brush holders are typically part of a brush assembly(ies). The brush holders and brushes are disposed diametrically opposite to each other with the commutator disposed therebetween. The brush assembly(ies) includes springs that urge the brushes against the commutator. Exemplary brush assemblies may utilize two or four brushes around the commutator.
Conventional brush assemblies often require the brushes opposite each other to be electrically connected. Connecting the brushes is particularly challenging in four-pole brush assemblies. Some conventional designs use brush holders mounted on the top surface of the brush assembly with metal routings on the back surface connecting the respective brush holders. Alternatively the brush holders may be connected via loose wires. Connecting the brush holders in this manner produces high connection resistance. What is needed is a reliable design that allows for lower connection resistance and more efficient manufacturability.
Another problem in conventional brush assemblies is the high level of tolerances between the armature and brush assembly components that lead to inefficient manufacturing. Some conventional brush assemblies utilize an intermediate piece between the shaft bearing of the armature shaft and the brush assembly, where the intermediate piece houses the shaft bearing and is secured to the brush assembly. This results in a larger tolerance between the relative positions of the brush assembly and shaft bearing, due to the tolerance of the intermediate piece. It is also desirable for the brush assembly and the shaft bearing to be assembled in a way that the tolerance between their relative positions is reduced.